1. Field of Invention
This invention pertains to a method and system for producing double-sided multi-layer optical discs. The method consists of producing several master discs, one for each data layer. The master discs come in two sets: one set for the layers on one side of the disc, and another set for the layers on the other side of the disc. The master discs of the two sets have their data arranged along opposite spirals, the two spirals being mirror images of each other.
2. Description of the Prior Art
A double-sided multiple-layer optical disc, such as a DVD, has a very large digital data storage capacity. For example, a DVD-18 having two data layers on each side can be used to store about 18 GB of data. Therefore, double-sided DVDs are becoming the favorite medium for recording and distributing multimedia programming, such as movies. A double-sided optical disc can store the visual portion of the programming, the audio portion in one or more languages, and various additional information that may be related to the programming.
Typically, DVDs are read by players that are capable of reading only one side at a time. A DVD is first inserted into the player with its first side oriented toward the read head. The player detects that the DVD is present and directs its read head to read data from one of the layers (typically, the outer layer) while the DVD is rotated in a preselected direction. When the player is finished reading data from the first side (one or both layers), the user removes the DVD, flips it upside down and reinserts it with the second side facing the read head. The player then directs its head to read the data from one or both layers of the second side.
One major problem with this whole process is that data cannot be read from both sides of the DVD seamlessly since the DVD must be physically removed from the player and flipped around. A further disadvantage is that data cannot be read from the two sides simultaneously.
As far as presently known, the only device that has two (or more) heads and reads both sides of a disc while the disc is rotated in a single direction is a magnetic hard drive. However, the disc for a magnetic hard drive has only one layer of information on each side. Moreover, the data on the disc is arranged in concentric circles rather than spiral tracks, and therefore, the drive needs a reading mechanism that is much simpler and far less accurate then the reading mechanisms used in an optical disc player.
DVD writers are known in the art that are capable of writing information on DVD blanks, however, they have only a single head and write only on one side at a time. Once data is written on one side, the disc is flipped over and data is written on the other side, in the opposite direction, so that it can be read by standard DVD players.
Automated assembly lines are also known that can produce double-sided DVDs that have two layers at least on one side. However, these assembly lines produce DVDs with data arranged along spirals oriented in the same direction when viewed from the respective sides.